Development of emission factors and efficiency of two nitrification inhibitors, DCD and DMPP

Nitrous oxide (N2O) is a powerful greenhouse gas (GHG). The main sources of N2O emissions are nitrogen fertilizer and manure applications to agricultural fields. Many field studies have tested the effectiveness of nitrification inhibitors (NIs) to reduce N2O emissions but results varied considerably because the studies were carried out under different climate and soil conditions. We conducted this analysis (consisting of 111 datasets from 39 studies published in peer-reviewed journals up to 2014) about two of the most common Nis. Dicyadiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) were studied to determine the variability in their efficiency and the effect of environmental parameters on this efficiency under field conditions. Both Nis were effective in reducing N2O emissions; the inhibitory effect for DCD was 42.3% +/- 2.2 and for DMPP was 40.2% +/- 3.7, with emission factors (EF) for N amendment with DCD or DMPP of 0.41% +/- 0.05 and 0.7% +/- 0.33, respectively. We also analysed the EF and the inhibitory effect across four different land uses, seven different soil textures and ten fertilizer types. The lowest EF for the NI-amended treatments was for paddy followed by upland and cropland and the highest for grassland. Our meta-analysis showed the highest inhibitory effect was on grassland (40.9% +/- 5.4, 95% confidence interval (CI) 29.0% to 52.9%) followed by cropland (34.3% +/- 4.6,95% Cl 23.6% to 46.0%), upland 27.0% +/- 4.5 (95% CI 16.5% to 36.9%) and paddy 26.5% +/- 6.9(95% Cl 5.5% to 47.6%). In-general, soil textures with low clay content (less than 50%) and with sand content greater than 50% had the lowest EFs. However, soil texture had little effect on the inhibitory effect. In addition, both Nis were effective with almost all fertiliser types included in the analysis. (C) 2015 Elsevier B.V. All rights reserved.